Adult RSV hospitalizations in Spain: clinical characteristics and risk factors for ICU admission, prolonged stay, and mortality across six seasons (2016–2017 to 2021–2022)

Objective To describe the clinical characteristics of adults hospitalized with respiratory syncytial virus (RSV) in Spain over six epidemiological seasons (2016–2017 to 2021–2022) and identify factors associated with ICU admission, prolonged length of stay, and in-hospital mortality (IHM). Methods Retrospective, population-based study in adults (≥15 years) hospitalized for RSV and included in the Spanish hospital discharge database (containing all records of hospitalizations in Spain). Factors linked to ICU admission, prolonged length of stay, and IHM were assessed using multivariable logistic regression. Results A total of 20,695 adults (56.5% women) were hospitalized with RSV. Case numbers increased until 2018–2019, then declined during the COVID-19 pandemic. Patients aged 15–64 years accounted for 20.9% of the sample; 65–79 years, 31.2%; and ≥80 years, 47.9%. Common comorbidities included hypertension (61.3%), diabetes (28.0%), and heart failure (26.1%). ICU admission (6.4% of cases) was independently associated with age 15–64 years (adjusted odds ratio [aOR] 5.04, 95% confidence interval [CI] 4.21–6.03), COVID-19 co-infection (aOR 5.06, 95% CI 2.88–8.87), and RSV pneumonia (aOR 2.19, 95% CI 1.48–3.27). IHM increased with age (15–64 years: 4.0%; 65–79 years: 6.2%, aOR 1.67, 95% CI 1.37–2.04; and ≥80 years: 9.5%, aOR 3.32, 95% CI 2.73–4.04). Other key risk factors were ICU admission (aOR 6.23, 95% CI 5.30–7.33), leukemia (aOR 3.31, 95% CI 2.11–4.59), and neoplasm (aOR 2.90, 95% CI 2.43–3.47). Conclusions RSV represents a significant and growing burden among hospitalized adults, particularly in older individuals and those with underlying comorbidities, who experience worse outcomes and higher mortality. These findings underscore the importance of prevention strategies, including vaccination of adults aged ≥60 years and high-risk groups.